CN112785982B - Display device - Google Patents

Abstract

Translated fromChinese

本公开涉及一种显示装置，包括：多个像素，以及控制电路；其中，多个像素中的至少一个像素包括：包括阳极和阴极的发光元件；电容器；采样晶体管，被配置为根据通过采样控制信号线供应的采样控制信号将信号电压从数据信号线供应至电容器；驱动晶体管，被配置为根据存储在电容器中的电压将驱动电流从第一电压线供应至阳极；第一晶体管，电连接在阳极与第二电压线之间；第二晶体管，电连接在第一电压线与驱动晶体管之间；及电压控制元件，被配置为控制驱动晶体管的栅极与驱动晶体管的源极之间的电位差；采样晶体管和第一晶体管被配置为在第一定时导通，采样晶体管被配置为在第二晶体管处于截止状态的第一状态期间多次截止，第一状态在第一定时之后。

The present disclosure relates to a display device, comprising: a plurality of pixels, and a control circuit; wherein at least one of the plurality of pixels comprises: a light emitting element comprising an anode and a cathode; a capacitor; a sampling transistor configured to supply a signal voltage from a data signal line to the capacitor according to a sampling control signal supplied through a sampling control signal line; a driving transistor configured to supply a driving current from a first voltage line to the anode according to a voltage stored in the capacitor; a first transistor electrically connected between the anode and a second voltage line; a second transistor electrically connected between the first voltage line and the driving transistor; and a voltage control element configured to control a potential difference between a gate of the driving transistor and a source of the driving transistor; the sampling transistor and the first transistor are configured to be turned on at a first timing, and the sampling transistor is configured to be turned off a plurality of times during a first state in which the second transistor is in an off state, the first state being after the first timing.

Description

Display device

The present application is a divisional application of PCT application of chinese national stage application having application date 2015, 8-31, international application number PCT/JP2015/074700, title of the application "display device, method for driving the display device, and electronic device", which enters chinese national stage at entry date 2017, 4-26, application number 201580058235.9, incorporated herein by reference in its entirety.

Technical Field

The present disclosure relates to a display device, a method for driving the display device, and an electronic device.

Background

Recently, in the field of display devices, flat panel display devices in which pixels (pixel circuits) including light emitting units are two-dimensionally arranged in a matrix form have become mainstream. In this flat panel display device, characteristics of a transistor driving a light emitting unit may vary for each pixel due to variations in process or the like. The characteristic variation of the transistor driving the light emitting unit affects the light emitting luminance.

Specifically, even if video signals of the same level (signal voltage) are written to each pixel, the light emission luminance varies between pixels. Therefore, the generator displays unevenness, and then uniformity of the display screen is deteriorated. Accordingly, a function for correcting display unevenness due to a characteristic change or the like of a driving transistor driving a light emitting unit is provided in the display device. Further, the correction operation is performed during a period in which the writing transistor writing the video signal is in an on state. The correction period for performing the correction operation is determined by the capacitance value (capacitive pixel) of the pixel capacitor.

However, in the display device having the above correction function, there are cases in which: when the source voltage of the driving transistor varies during the correction operation, it is necessary to shorten the correction period (correction time). The correction period is determined by the pulse width of the driving pulse driving the writing transistor. Therefore, the correction period can be shortened by shortening the pulse width of the driving pulse. Accordingly, in the related art, a pulse width adjustment circuit is formed on a display panel to generate a pulse signal whose pulse width is shortened based on a pulse signal input from the outside, and the pulse signal is used as a driving pulse (for example, see PTL 1).

List of citations

Patent literature

Patent document 1: JP 2012-255875A

Disclosure of Invention

Technical problem

However, according to the related art disclosed in patent document 1, since a pulse width adjustment circuit for generating a driving pulse whose pulse width is shortened needs to be formed on the display panel, the circuit size of a peripheral circuit driving the pixel circuit increases. As a result, since the area of the peripheral circuit region (i.e., a so-called bezel region) of the pixel array unit on the display panel provided with the peripheral circuit increases, this hinders miniaturization of the display panel.

The present disclosure is directed to providing a display device in which a pulse width of a driving pulse does not need to be shortened and a circuit size of a peripheral circuit of a pixel array can be reduced, a method for driving the display device, and an electronic device including the display device.

Solution to the problem

In order to achieve the above object, a display device according to the present disclosure includes:

A pixel array unit in which pixel circuits each including a light emitting unit, a writing transistor that writes a signal voltage of a video signal, a holding capacitor that holds the signal voltage written by the writing transistor, a driving transistor that drives the light emitting unit based on the signal voltage held by the holding capacitor, and an auxiliary capacitor having one end connected to a source node of the driving transistor, the pixel circuit having a function of threshold correction processing are arranged in a matrix form: the threshold correction process changes a source voltage of the driving transistor toward a voltage obtained by subtracting a threshold voltage of the driving transistor from an initialization voltage with reference to the initialization voltage of the gate voltage of the driving transistor; and

And a control unit that sets an operating point of the driving transistor to an off-region by supplying a potential change to a source electrode of the driving transistor through coupling via the auxiliary capacitor after the threshold correction process.

Further, in order to achieve the above object, an electronic device according to the present disclosure includes a display device having the above configuration.

In order to achieve the above object, according to the present disclosure, a method for driving a display device including a pixel array unit in which pixel circuits each including a light emitting unit, a writing transistor that writes a signal voltage of a video signal, a holding capacitor that holds the signal voltage written by the writing transistor, a driving transistor that drives the light emitting unit based on the signal voltage held by the holding capacitor, and an auxiliary capacitor having one end connected to a source node of the driving transistor, the pixel circuit having a function of threshold correction processing: the threshold correction process changes a source voltage of the driving transistor toward a voltage obtained by subtracting a threshold voltage of the driving transistor from an initialization voltage with reference to the initialization voltage of the gate voltage of the driving transistor, the method including:

When driving the display device, an operating point of the driving transistor is set to an off region by supplying a potential change to a source electrode of the driving transistor through coupling of the auxiliary capacitor after the threshold correction process.

In the display device, the method for driving the display device, and the electronic device having the above-described configuration, when the signal voltage is written by the writing transistor, since the operating point of the driving transistor is the off-region, the current does not naturally flow into the driving transistor. Accordingly, a factor that causes source voltage fluctuation of the driving transistor other than coupling associated with writing of the signal voltage can be eliminated. Therefore, there is no need to shorten the correction period (correction time), and thus there is no need to narrow the pulse width of the driving pulse.

In one embodiment, the present disclosure relates to a display device including: a plurality of pixels, and a control circuit; wherein at least one of the plurality of pixels includes: a light emitting element including an anode and a cathode; a capacitor; a sampling transistor configured to supply a signal voltage from the data signal line to the capacitor according to a sampling control signal supplied through the sampling control signal line; a driving transistor configured to supply a driving current from a first voltage line to an anode according to a voltage stored in the capacitor; a first transistor electrically connected between the anode and a second voltage line; a second transistor electrically connected between the first voltage line and the driving transistor; and a voltage control element configured to control a potential difference between a gate of the driving transistor and a source of the driving transistor; the sampling transistor and the first transistor are configured to be turned on at a first timing, and the sampling transistor is configured to be turned off a plurality of times during a first state in which the second transistor is in an off state, the first state being after the first timing.

Wherein the voltage control element is electrically connected in series to the capacitor.

Wherein the voltage control element is configured to control a potential difference between the gate of the driving transistor and the source of the driving transistor in accordance with a voltage control signal supplied through the voltage control signal line; and the sampling control signal line and the voltage control signal line are formed to have the same thickness and width.

Wherein the first transistor is configured to electrically connect the anode and the second voltage line according to a first control signal supplied through the first control signal line; and the second transistor is configured to electrically connect the first voltage line and the driving transistor according to a second control signal supplied through the second control signal line.

Wherein the sampling transistor, the driving transistor, the first transistor and the second transistor are P-channel transistors.

Wherein the potential of the first voltage line is higher than the potential of the second voltage line.

Wherein the voltage control element comprises an auxiliary capacitor.

Wherein the cathode is electrically connected to a third voltage line.

The control circuit comprises a first control circuit and a second control circuit; and a plurality of pixels are arranged between the first control circuit and the second control circuit.

Advantageous effects of the present disclosure

According to the present disclosure, it is not necessary to shorten the pulse width of the driving pulse, and thus the circuit size of the peripheral circuit of the pixel array can be reduced.

Note that the present disclosure is not limited to exhibiting the effects described herein, and may exhibit any of the effects described in the present specification. In addition, the effects described in the present specification are not limiting but merely examples, and there may be additional effects.

Drawings

Fig. 1 is a system configuration diagram showing an outline of a basic configuration of an active matrix organic EL display device which is a premise of the present disclosure.

Fig. 2 is a circuit diagram showing a circuit configuration of a 2Tr2C unit pixel (pixel circuit).

Fig. 3 is a timing waveform diagram for describing basic circuit operation in an ideal state of an active matrix organic EL display device as a premise of the present disclosure.

Fig. 4A and 4B are waveform diagrams showing mobility correction operations, in which fig. 4A shows an operation example in the case where the current supply capability of the driving transistor is large and the capacitance value of the pixel capacitor is small, and fig. 4B shows an operation example in the case where the mobility correction time is shortened.

Fig. 5 is a circuit diagram showing a configuration example of a pulse width adjustment circuit in a peripheral circuit of the pixel array unit.

Fig. 6 is a timing waveform diagram showing waveforms of signals of respective units in fig. 5.

Fig. 7 is a system configuration diagram showing an outline of the configuration of an organic EL display device including a pixel circuit according to example 1.

Fig. 8 is a timing waveform diagram for describing the circuit operation of the organic EL display device including the pixel circuit according to example 1.

Fig. 9 is a system configuration diagram showing an outline of the configuration of an organic EL display device including a pixel circuit according to example 2.

Fig. 10 is a timing waveform diagram for showing the circuit operation of the organic EL display device including the pixel circuit according to example 2.

Fig. 11A is a front view of a lens-interchangeable single-lens reflex digital camera, and fig. 11B is a rear view of the lens-interchangeable single-lens reflex digital camera.

Fig. 12 is an external view of the head-mounted display.

Detailed Description

Hereinafter, preferred embodiments (which will be hereinafter described as "embodiments") for implementing the techniques of the present disclosure will be described in detail with reference to the accompanying drawings. The technology of the present disclosure is not limited to the embodiments, and various values and materials shown in the embodiments are examples. In the description provided below, structural elements having substantially the same functions and structures are denoted by the same reference numerals, and repeated explanation of these structural elements is omitted. It should be noted that the description will be provided in the following order.

1. Display device, method of driving display device, and general description of electronic device of the present disclosure

2. Display device as premise of the present disclosure

2-1 System configuration

2-2 Pixel Circuit

2-3 Basic circuit operation in an ideal state

2-4. Shorten mobility correction time

2-5 Pulse width adjusting circuit

3. Display device according to embodiments of the present disclosure

3-1 Example 1 (example in which the pixel Circuit is made up of N-channel type transistors)

3-2 Example 2 (example where the pixel Circuit is made up of P-channel type transistors)

4. Electronic device

4-1. Specific example 1 (example of digital camera)

4-2 Specific example 2 (example of head mounted display)

< General description of display device, method for driving display device, and electronic device of the present disclosure >

In the display device, the method for driving a display device, and the electronic device of the present disclosure, a configuration may be used in which the control unit changes the potential of the source electrode of the driving transistor by supplying a potential change to the other end of the auxiliary capacitor. Further, when the other end of the auxiliary capacitor is connected to the control line, a configuration may be used in which the control unit switches the control signal supplied to the other end of the auxiliary capacitor from the inactive state to the active state through the control line, thereby supplying a potential change to the source electrode of the driving transistor.

In the display device, the method for driving a display device, and the electronic device of the present disclosure having the above-described preferred configurations, a configuration may be used in which the source voltage of the driving transistor is a voltage at least less than the sum of the cathode voltage of the light emitting unit and the threshold voltage of the light emitting unit when a potential change is supplied to the source electrode of the driving transistor. Further, a configuration may be used in which the write transistor writes a signal voltage to the gate electrode of the drive transistor after a potential change is supplied to the source electrode of the drive transistor.

Further, in the display device, the method for driving a display device, and the electronic device of the present disclosure having the above-described preferred configurations, a configuration may be used that includes a write scan unit that drives the write transistor by scan lines in units of rows. Here, it is preferable that the control unit and the write scan unit are disposed in a peripheral circuit region on the same side with respect to the pixel array unit. Further, it is preferable that the control line and the scan line are formed of the same wire material and have the same thickness and width.

Alternatively, in the display device, the method for driving a display device, and the electronic device of the present disclosure having the above-described preferred configurations, a configuration may be used in which when the threshold correction process and the write signal voltage enter the active state twice during the write scan signal enter the active state twice, the pulse widths of the two pulses are the same. Further, a configuration may be used in which the pixel circuit performs mobility correction processing in the period of the second pulse among the two pulses. The mobility correction process is a process of correcting the mobility of the driving transistor by applying negative feedback of a correction amount corresponding to the current flowing through the driving transistor to the potential difference between the gate electrode and the source electrode of the driving transistor.

< Display device as a premise of the present disclosure >

[ System configuration ]

Fig. 1 is a system configuration diagram showing an outline of a basic configuration of an active matrix organic EL display device which is a premise of the present disclosure.

An active matrix display device is a display device in which driving of a light emitting unit (light emitting element) is performed by an active element, such as an insulated gate field effect transistor, provided in the same pixel as the light emitting unit. In general, a Thin Film Transistor (TFT) may be used as the insulated gate field effect transistor.

Here, a case in which an active matrix organic EL display device uses an organic EL element as a light emitting unit (light emitting element) of a unit pixel (pixel circuit) will be described as an example. The organic EL element is a current-driven electro-optical element whose light emission luminance varies according to the value of current flowing through the device. Hereinafter, "unit pixel/pixel circuit" is simply described as "pixel" in some cases. The thin film transistor is used not only for controlling a pixel but also for controlling a peripheral circuit which will be described below.

As shown in fig. 1, an active matrix organic EL display device 10 which is a premise of the present disclosure is configured to include a pixel array unit 30, the pixel array unit 30 being configured such that a plurality of unit pixels 20 are two-dimensionally arranged in a matrix form (matrix state), and a driving unit (peripheral circuit) which is provided in a peripheral region of the pixel array unit 30 and drives the pixels 20. The driving unit is constituted by, for example, the write scanning unit 40, the power scanning unit 50, and the signal output unit 60, and drives the pixels 20 of the pixel array unit 30.

In this example, the write scan unit 40, the power scan unit 50, and the signal output unit 60 are mounted on the same substrate as the pixel array unit 30, i.e., on the display panel 70, as peripheral circuits of the pixel array unit 30. However, a configuration may be adopted in which some or all of the write scan unit 40, the power supply scan unit 50, and the signal output unit 60 are disposed outside the display panel 70. Further, a configuration in which the write scan unit 40 and the power scan unit 50 are both provided on one side of the pixel array unit 30 is used, or a configuration in which the write scan unit 40 and the power scan unit 50 are provided with the pixel array unit 30 interposed therebetween may be used. As the substrate of the display panel 70, a transparent insulating substrate such as a glass substrate may be used, or a semiconductor substrate such as a silicon substrate may be used.

Here, when the organic EL display device 10 performs color display, one pixel (unit pixel) serving as one unit at the time of forming a color image is constituted by sub-pixels of a plurality of colors. In this case, each sub-pixel corresponds to the pixel 20 of fig. 1. More specifically, in a display device that performs color display, one pixel is constituted of, for example, three sub-pixels including a sub-pixel that emits red (R) light, a sub-pixel that emits green (G) light, and a sub-pixel that emits blue (B) light.

However, one pixel is not limited to the combination of the sub-pixels having three primary colors including RGB, and sub-pixels having one or more colors may be added to the sub-pixels having three primary colors to form one pixel. More specifically, the luminance can be increased by adding sub-pixels emitting white (W) light to form one pixel, or the color reproduction range can be extended by adding at least one sub-pixel emitting light of a complementary color to form one pixel.

In the pixel array unit 30, for each pixel, the scanning lines 31 (31₁～31_m) and the power supply lines 32 (32₁～32_m) are wired in an array of m rows and n columns of pixels 20 in a row direction (a pixel array direction of a pixel row or a horizontal direction). Further, for each pixel, the signal line 33 (33₁～33_n) is wired on the array of the pixels 20 of m rows and n columns in the column direction (pixel array direction of the pixel column or vertical direction).

Scan lines 31₁～31_m are connected to respective output terminals of respective rows of write scan cells 40. The power supply lines 32₁～32_m are connected to respective output terminals of respective rows of the power supply scan cells 50. The signal lines 33₁～33_n are connected to output terminals of the corresponding columns of the signal output units 60.

The write scanning unit 40 is constituted by a shift register circuit or the like. When writing the signal voltage of the video signal onto each pixel 20 of the pixel array unit 30, the write scanning unit 40 performs so-called line sequential scanning in which each pixel 20 of the pixel array unit 30 is scanned in line units in order by sequentially supplying the write scanning signal WS (WS₁～WS_m) to the scanning line 31 (31₁～31_m).

Similar to the write scan unit 40, the power supply scan unit 50 is constituted by a shift register circuit or the like. In synchronization with the line sequential scanning performed by the write scanning unit 40, the power scanning unit 50 supplies the power line 32 (32₁～32_m) with a power supply voltage DS (DS₁～DS_m) switchable between a first power supply voltage V_ccp and a second power supply voltage V_ini lower than the first power supply voltage V_ccp. As will be described later, the light emission and non-light emission (off) of the pixel 20 are controlled by switching the power supply voltage DS between V_ccp and V_ini.

The signal output unit 60 selectively outputs a signal voltage V_sig (which may be simply referred to as a "signal voltage" hereinafter) of the video signal, which is based on luminance information and a reference voltage V_ofs supplied from a signal supply source (not shown). Here, the reference voltage V_ofs is a voltage serving as a reference of the signal voltage V_sig of the video signal (for example, a voltage equivalent to the black level of the video signal), and is used in threshold correction processing described later.

The signal voltage V_sig and the reference voltage V_ofs output from the signal output unit 60 are written in each pixel 20 of the pixel array unit 30 via the signal line 33 (33₁～33_n) in units of pixel rows selected by the scanning performed by the write scanning unit 40. In other words, the signal output unit 60 adopts a driving form in which the signal voltages V_sig are written in line order written in units of rows (lines).

[ Pixel Circuit ]

Fig. 2 is a circuit diagram showing an example of a detailed circuit configuration of the unit pixel (pixel circuit) 20. The light emitting unit of the pixel 20 is constituted by an organic EL element 21, and the organic EL element 21 is an example of a current-driven electro-optical element whose light emission luminance varies according to the value of the current flowing through the device.

As shown in fig. 2, the pixel 20 includes an organic EL element 21 and a driving circuit that drives the organic EL element 21 by applying a current to the organic EL element 21. The cathode electrode of the organic EL element 21 is connected to a common power supply line 34 which is commonly wired for all the pixels 20.

The driving circuit that drives the organic EL element 21 has a 2Tr2C circuit configuration including a driving transistor 22, a writing transistor 23, a holding capacitor 24, and an auxiliary capacitor 25, that is, two transistors (T_r) and two capacitive elements (C). Here, an N-channel Thin Film Transistor (TFT) is used as the driving transistor 22 and the writing transistor 23. The conductive combinations of the driving transistor 22 and the writing transistor 23 mentioned here are merely examples, but the present disclosure is not limited to such combinations.

One electrode (source electrode or drain electrode) of the driving transistor 22 is connected to each power supply line 32 (32₁～32_m), and the other electrode (source electrode or drain electrode) thereof is connected to the anode electrode of the organic EL element 21. One electrode (source electrode or drain electrode) of the writing transistor 23 is connected to each signal line 33 (33₁～32_m), and the other electrode (source electrode or drain electrode) thereof is connected to the gate electrode of the driving transistor 22. In addition, a gate electrode of the writing transistor 23 is connected to each scanning line 31 (31₁～31_m).

Regarding the driving transistor 22 and the writing transistor 23, one electrode refers to a metal line electrically connected to one source region or drain region, and the other electrode refers to a metal line electrically connected to the other source region or drain region. In addition, one electrode may be a source electrode or a drain electrode, and the other electrode may be a drain electrode or a source electrode, according to a potential relationship between the electrode and the other electrode.

One electrode of the holding capacitor 24 is connected to the gate electrode of the driving transistor 22, and the other electrode thereof is connected to the other electrode of the driving transistor 22 and to the anode electrode of the organic EL element 21. One electrode of the auxiliary capacitor 25 is connected to the anode electrode of the organic EL element 21, and the other electrode thereof is connected to the cathode electrode of the organic EL element 21. That is, the auxiliary capacitor 25 is connected in parallel with the organic EL element 21.

In the above configuration, the writing transistor 23 enters the on state in which the state of the high voltage applied from the writing scanning unit 40 to the gate of the writing transistor 23 through the scanning line 31 becomes the active state in response to the writing scanning signal WS. Accordingly, the writing transistor 23 samples the signal voltage of the video signal V_sig or the reference voltage V_ofs according to the luminance information supplied from the signal output unit 60 through the signal line 33 at different points in time, and writes the voltage into the pixel 20. The signal voltage V_sig or the reference voltage V_ofs written by the writing transistor 23 is held by the holding capacitor 24.

When the power supply voltage DS of the power supply line 32 (32₁～32_m) becomes the first power supply voltage V_ccp, the driving transistor 22 operates in the saturation region because one electrode thereof serves as a drain electrode and the other electrode serves as a source electrode. Accordingly, the driving transistor 22 receives a supply of current from the power supply line 32, and then drives the organic EL element 21 to emit light by current driving. More specifically, the driving transistor 22 supplies a driving current of a current value corresponding to the voltage value of the signal voltage V_sig held in the holding capacitor 24 to the organic EL element 21 to drive the organic EL element 21 to emit light using the current.

Further, when the power supply voltage DS is switched from the first power supply voltage V_ccp to the second power supply voltage V_ini, the driving transistor 22 operates as a switching transistor because one electrode thereof serves as a source electrode and the other electrode thereof serves as a drain electrode. Accordingly, the driving transistor 22 stops the supply of the driving current to the organic EL element 21, thereby setting the organic EL element 21 to the non-light emitting state. In other words, the driving transistor 22 also has a function as a transistor that controls light emission and non-light emission of the organic EL element 21.

By switching the operation of the driving transistor 22, a period (non-emission period) in which the organic EL element 21 is in a non-emission state can be set, and the ratio (duty ratio) of the emission period and the non-emission period of the organic EL element 21 can be controlled. By the control of the duty ratio, afterimages and blurring caused by the pixels emitting light in one display frame period can be reduced, and in particular, the quality level of a dynamic image can be made more preferable.

Among the first power supply voltage V_ccp and the second power supply voltage V_ini selectively supplied from the power supply scanning unit 50 through the power supply line 32, the first power supply voltage V_ccp is a power supply voltage for supplying a driving current (for driving the organic EL element 21 to emit light) to the driving transistor 22. Further, the second power supply voltage V_ini is a power supply voltage for applying a reverse bias to the organic EL element 21. The second power supply voltage V_ini is set to a voltage lower than the reference voltage V_ofs, and for example, when the threshold voltage of the driving transistor 22 is set to V_th, the second power supply voltage Vini is set to a voltage lower than V_ofs-V_th, and preferably to a voltage sufficiently lower than V_ofs-V_th.

Each pixel 20 of the pixel array unit 30 has a function of correcting a variation in driving current caused by a variation in characteristics of the driving transistor 22. Here, for example, as characteristics of the driving transistor 22, a threshold voltage V_th of the driving transistor 22 and a mobility u of a semiconductor film constituting a channel of the driving transistor 22 (which will be simply referred to as "mobility u of the driving transistor 22" hereinafter) are exemplified.

Correction of the variation in the drive current caused by the variation in the threshold voltage V_th (which will be described as "threshold correction" hereinafter) is performed by initializing the gate voltage V_g of the drive transistor 22 to the reference voltage V_ofs. Specifically, the following operations are performed: the initialization voltage (reference voltage V_ofs) of the gate voltage V_g of the driving transistor 22 is set as a reference, and the source voltage V_s of the driving transistor 22 is changed to a potential obtained by: a potential obtained by lowering the threshold voltage V_th of the driving transistor 22 from the initialization voltage (reference voltage V_ofs). As this operation proceeds, the gate-source voltage V_gs of the driving transistor 22 quickly converges to the threshold voltage V_th of the driving transistor 22. A voltage equal to the threshold voltage V_th is held in the holding capacitor 24. By holding the voltage equal to the threshold voltage V_th in the holding capacitor 24, the dependence of the drain-source current I_ds flowing through the driving transistor 22 on the threshold voltage V_th when the driving transistor 22 is driven at the signal voltage V_sig of the video signal can be suppressed.

In a state where the writing transistor 23 is brought into an on state and the signal voltage V_sig of the video signal is written, correction of a variation in the driving current due to a variation in the mobility u (to be described as "mobility correction" hereinafter) is performed by flowing a current to the holding capacitor 24 via the driving transistor 22. In other words, correction is performed by applying negative feedback to the holding capacitor 24 by a feedback amount (correction amount) corresponding to the current I_ds flowing through the driving transistor 22. When the video signal is written by threshold correction, the dependence of the drain-source current_Ids on the threshold voltage V_th disappears, and the drain-source current I_ds depends on the mobility u of the driving transistor 22. Therefore, by applying negative feedback to the drain-source voltage V_ds of the driving transistor 22 in a feedback amount corresponding to the current I_ds flowing through the driving transistor 22, the dependence of the drain-source current I_ds flowing through the driving transistor 22 on the mobility u can be suppressed.

[ Basic Circuit configuration in ideal State ]

Fig. 3 is a timing waveform diagram for explaining the basic circuit operation of the organic EL display device 10 having the above configuration in an ideal state. In the timing waveform diagram of fig. 3, the respective changes of the voltage (write scan signal) WS of the scan line 31, the voltage (power supply voltage) DS of the power supply line 32, the voltage (V_sig/V_ofs) of the signal line 33, and the gate voltage V_g and the source voltage V_s of the drive transistor 22 are shown.

Since the write transistor 23 is of an N-channel type, the state of the high voltage of each write scan signal WS is an active state and the state of the low voltage thereof is an inactive state. Further, the write transistor 23 enters a conductive state in the write scan signal WS in an active state, and enters a non-conductive state in the write scan signal WS in a non-active state.

In the timing waveform diagram of fig. 3, a period from the time point t11 to the time point t19 is a switching period of the voltage of the signal line 33, that is, a switching period of the signal voltage V_sig and the reference voltage V_ofs of the video signal, and switching of the signal voltage V_sig and the reference voltage V_ofs is performed in 1 horizontal period (1H).

The time before the time point t₁₂ corresponds to the light-emitting period of the organic EL element 21 in the previous display frame. When the time reaches the time point t₁₂, a non-light-emitting period of a new display frame (current display frame) in the line-sequential scanning is started. Further, a period from the time point t₁₃ to the time point t₁₅ in which the write scan signal WS enters the activated state is a writing period in which the write transistor 23 writes the reference voltage V_ofs into the pixel 20. In addition, a period from a time point t₁₄ (at a time point t₁₄, the voltage DS of each power supply line 32 is switched from the second power supply voltage V_ini to the first power supply voltage V_ccp) to a time point t₁₅ (at a time point t₁₅, the write scan signal WS is converted into an inactive state) is a threshold correction period for correcting a variation in the drive current caused by a variation in the threshold V_th of the drive transistor 22.

Further, during a period from the time point t₁₆ to the time point t₁₉, the voltage of the signal line 33 becomes the signal voltage V_sig of the video signal. In addition, during the period from the time point t₁₇ to the time point t₁₈, the write scan signal WS enters the active state again, and the write transistor 23 enters the on state. Accordingly, the signal voltage V_sig of the video signal is written to the pixel 20 through the writing transistor 23, and mobility correction processing is performed to correct a variation in the drive current caused by a variation in the mobility u of the drive transistor 22. That is, the period from the time point t₁₇ to the time point t₁₈ is a writing and mobility correction period of the signal voltage V_sig. Then, when the time reaches the time point t₁₈, the light-emitting period of the current frame starts.

In the timing waveform diagram of fig. 3, V_cath is the cathode voltage of the organic EL element 21. Further, V_thel is a threshold voltage of the organic EL element 21.

[ Shortening mobility correction time ]

In the above-described organic EL display device 10, the variation in the source voltage of the driving transistor 22 in the mobility correction operation is determined by the relationship between the current supply capability of the driving transistor 22 and the capacitance value of the pixel capacitor connected to the source electrode of the driving transistor 22. Specifically, the source voltage V of the driving transistor 22 after the mobility correction operation is given as the following expression (1).

Here, V_sig denotes a signal voltage of the video signal, V_th denotes a threshold voltage of the driving transistor 22, V_s denotes a source voltage of the driving transistor 22 before the mobility correction operation, t denotes a mobility correction time, and β denotes a current supply capability of the driving transistor 22. Further, C represents the capacitance value of the pixel capacitor. In addition, when the capacitance value of the holding capacitor 24 is C_s, the capacitance value of the equivalent capacitor of the organic EL element 21 is C_oled, and the capacitance value of the auxiliary capacitor 25 is C_sub, c=c_s+C_oled+C_sub. Further, the current supply capability β of the driving transistor 22 is given as expression β=u×c_ox × (W/L). Here, u denotes mobility of a semiconductor film forming a channel of the driving transistor 22, C_ox denotes gate capacitance per unit area of the driving transistor 22, W denotes channel width, and L denotes channel length.

As understood from expression (1), as the current supply capability β of the driving transistor 22 increases and the capacitance value C of the pixel capacitor decreases, the increase (V_s →v) in the source voltage of the driving transistor 22 at the same mobility correction time t becomes large.

That is, as shown in fig. 4A, in the case where the current supply capability β of the driving transistor 22 is large and the capacitance value C of the pixel capacitor is small, the rate of increase of the source voltage V_s of the driving transistor 22 under the mobility correction operation is accelerated, and thus the source voltage V_s can reach the voltage value V_cath+V_thel during writing of the signal voltage V_sig. Further, since a current starts to flow in the organic EL element 21 at the timing when the source voltage V_s of the driving transistor 22 reaches the voltage value V_cath+V_thel, mobility correction cannot be properly performed or the organic EL element 21 erroneously emits light, which becomes a factor of uniformity deterioration.

Therefore, as shown in fig. 4B, a driving method for shortening the mobility correction time (signal writing and mobility correction period) and terminating the mobility correction operation before the current starts to flow in the organic EL element 21 (i.e., before the organic EL element 21 is turned on) is considered. The mobility correction time is determined by the pulse width of the mobility correction pulse (i.e., the second pulse of the write scan signal WS in the timing waveform diagram of fig. 3). Therefore, the mobility correction time can be shortened by shortening the pulse width of the mobility correction pulse. Further, according to this driving method, deterioration of uniformity due to conduction of the organic EL element 21 during the mobility correction period can be suppressed.

However, in order to realize the driving for terminating the mobility correction operation before the above-described driving (i.e., before turning on the organic EL element 21), it is necessary to provide a circuit for generating a mobility correction pulse having a narrow (short) pulse width. In general, a pulse signal of a pulse width of about several hundred nanoseconds is input to the display panel 70 and generation of the write scan signal WS including the mobility correction pulse is performed in the display panel 70 based on the pulse signal. In this case, in order to shorten the pulse width of the mobility correction pulse, specifically, in order to generate the mobility correction pulse having a pulse width of about several nanoseconds, it is necessary to form a pulse width adjustment circuit on the display panel 70.

[ Pulse Width adjustment Circuit ]

Fig. 5 shows a configuration example of a pulse width adjustment circuit in the peripheral circuit of the pixel array unit 30. Fig. 5 shows the pixel array unit 30 and the write scanning unit 40 as one peripheral circuit thereof.

The write scanning unit 40 is constituted by, for example, a shift register circuit, and outputs shift signals WSSR₁～WSSR_m from the respective shift stages based on a cross pulse WSCK and a start pulse WSST input from the outside of the display panel 70 through the input terminals 71 and 72. The shift signal WSSR₁～WSSR_m is supplied to the respective pixel rows of the pixel array unit 30 as the write scan signal WS₁～WS_m including the mobility correction pulse through the switch circuit 41₁～41_m provided for each pixel row.

Further, the enable signals WSEN₁ and WSEN₂ are input to peripheral circuits on the display panel 70 through the input terminals 73 and 74. The pulse width of the enable signals WSEN₁ and WSEN₂ is about several hundred nanoseconds. The enable signals WSEN₁ and WSEN₂ are supplied to the pulse width adjustment circuit 80 through level shift (L/S) circuits 75 and 76. The pulse width adjustment circuit 80 is configured by a delay circuit unit 81 and a gate circuit unit 82.

The delay circuit unit 81 is a circuit portion for determining the pulse width of the mobility correction pulse, and has a configuration in which a plurality of inverter circuits are connected in series. The gate circuit unit 82 is configured by a nand circuit 821, an inverter circuit 822, a nor circuit 823, and an inverter circuit 824. The nand circuit 821 receives an input signal and an output signal of the delay circuit unit 81 as two inputs. The output signal of the nand circuit 821 becomes one input signal a of the nor circuit 823 through the inverter circuit 822. The pulse width of the input signal a is about several nanoseconds and becomes the pulse width of the mobility correction pulse.

Nor circuit 823 receives enable signal WSEN₂ that has passed through level shift circuit 76 as another input signal. The output signal of the nor circuit 823 is supplied to the buffer circuit 83 through the inverter circuit 824. The buffer circuit 83 has a configuration in which a plurality of inverter circuits are connected in series. The output signal B of the buffer circuit 83 is supplied to the switch circuit 41₁～41_m.

Fig. 6 shows waveforms of signals of the respective units in fig. 5. Specifically, fig. 6 shows respective waveforms of one input signal a of the cross pulse WSCK, the start pulse WSST, the enable signals WSEN₁ and WSEN₂, or the nor circuit 823, and the output signal B of the buffer circuit 83. Fig. 6 additionally shows respective waveforms of shift signals WSSR₁、WSSR₂、WSSR₃ and WSSR₄ corresponding to four pixel rows of the write scan unit 40 and write scan signals WS₁、WS₂、WS₃ and WS₄ corresponding to the four pixel rows.

As described above, in order to shorten the pulse width of the mobility correction pulse, the pulse width adjustment circuit 80 having the above configuration needs to be formed on the display panel 70. In addition, when the write scan signal WS is output to each pixel 20 of the pixel array unit 30, it is also necessary to increase the element size of the switching circuit 41₁～41_m to prevent pulse delay. If the element size is increased, parasitic capacitance attached to the wiring connected to the drain electrode (source electrode) of each switch circuit 41₁～41_m increases, and therefore, the element size of the buffer circuit 83 needs to be increased.

In this way, in order to shorten the pulse width of the mobility correction pulse, it is necessary to form the pulse width adjustment circuit 80 on the display panel 70 or to increase the element size of the buffer circuit 83, so that the circuit size of the peripheral circuit of the pixel array unit 30 increases. Accordingly, the area of the peripheral circuit region (i.e., the area of the bezel region) of the pixel array unit 30 in which the peripheral circuits are disposed on the display panel 70 increases. Further, when a configuration is adopted in which a semiconductor substrate such as a silicon substrate is used as the substrate of the display panel 70, the yield (theoretical yield) decreases, which results in an increase in the cost of the display device.

< Display device according to embodiments of the present disclosure >

In the active matrix type organic EL display device according to the embodiment of the present disclosure, it is not necessary to shorten the pulse width of the mobility correction pulse (driving pulse), and in order to be able to reduce the circuit size of the peripheral circuit of the pixel array unit, the operating point of the driving transistor 22 is set to the off region after the threshold correction process. Specifically, a potential change with respect to the source electrode of the driving transistor 22 is provided by coupling (so-called capacitive coupling) of the auxiliary capacitor 25, thereby setting the operating point of the driving transistor 22 as the off-region.

By supplying a potential change to the other end of the auxiliary capacitor 25, in which one end of the auxiliary capacitor 25 is connected to the source electrode of the driving transistor 22, the potential of the source electrode of the driving transistor 22 can be changed. More specifically, by connecting the other end of the auxiliary capacitor 25 to a control line and switching the control signal OS supplied to the other end of the auxiliary capacitor 25 from an inactive state to an active state through the control line, a potential change can be supplied to the source electrode of the driving transistor 22.

When a potential change is supplied to the source electrode of the driving transistor 22, the source voltage of the driving transistor 22 is set to a voltage at least smaller than V_cath+V_thel. Here, V_cath is a cathode electrode of the organic EL element 21, and V_thel is a threshold voltage of the organic EL element 21. The source voltage of the driving transistor 22 at this time is set as follows.

When the gate-source voltage of the driving transistor 22 after the potential change is supplied is denoted as V_gs'(＝V_g'-V_s '), the source voltage V_s' is set to a voltage satisfying the following expression.

Here, when the magnitude of the control signal OS is expressed as Δv_os, if the following expression is used,

The gate voltage V_g' of the driving transistor 22 is as follows.

Here, C_p denotes a parasitic capacitance formed in the gate electrode of the write transistor 23.

Further, when the maximum voltage of the signal voltage V_sig of the video signal is known, voltage setting is performed so that the driving transistor 22 remains in an off state even when the maximum voltage is written. Specifically, the voltage setting is performed as follows. Here, when the maximum voltage of the signal voltage V_sig of the video signal is denoted as V_sigMAX, the gate-source voltage of the driving transistor 22 after the signal voltage V_sig is set to a voltage satisfying the following expression.

V_g"＝V_sigMAX

As described above, by setting the operating point of the driving transistor to the off-region after the threshold correction process, the following effects can be obtained. After the threshold correction process, when the signal voltage V_sig of the video signal is written by the writing transistor 23, if the operating point of the driving transistor 22 is the off-region, the current I_ds does not naturally flow into the driving transistor 22. It is possible to eliminate a factor that fluctuates the source voltage V_s of the drive transistor 22 (this factor is different from the coupling associated with writing of the signal voltage V_sig). Therefore, there is no need to shorten the correction period (correction time), and thus there is no need to narrow the pulse width of the mobility correction pulse (driving pulse).

The fact that the pulse width of the mobility correction pulse does not need to be narrowed means that the pulse width adjustment circuit 80 (see fig. 5) for shortening the pulse width of the mobility correction pulse does not need to be formed on the display panel 70. Accordingly, a reduction in circuit size of the peripheral circuits of the pixel array unit 30 can be achieved. Further, since the circuit size of the peripheral circuit of the pixel array unit 30 is reduced, the frame of the display panel 70 can be narrowed as compared with the case where the pulse width of the mobility correction pulse is shortened, thereby reducing the size of the display panel 70. Further, when a configuration is adopted in which a semiconductor substrate such as a silicon substrate is used as the substrate of the display panel 70, it is promising to improve the yield, and thus it can contribute to the reduction of the cost of the display device.

The above-described technique of the present disclosure can be applied not only to the case where the transistor forming the pixel (pixel circuit) 20 is formed of an N-channel type transistor but also to the case where the transistor is formed of a P-channel type transistor. Hereinafter, a pixel circuit formed of an N-channel type transistor will be described as the pixel circuit according to example 1, and a pixel circuit formed of a P-channel type transistor will be described as the pixel circuit according to example 2. As will be apparent from the following description, the pixel circuit according to example 1 has an advantage in that the number of components of the pixel circuit is smaller than that of the pixel circuit according to example 2.

EXAMPLE 1

Fig. 7 is a system configuration diagram showing an outline of the configuration of an organic EL display device including a pixel circuit according to example 1.

Basically, the pixel circuit 20A according to example 1 is configured to have the same components as the pixel 20 shown in fig. 2. Specifically, the pixel circuit 20A includes an organic EL element 21, a driving transistor 22, a writing transistor 23, a holding capacitor 24, and an auxiliary capacitor 25. The driving transistor 22 and the writing transistor 23 are formed of N-channel MOS transistors. The pixel circuit 20A is different from the pixel 20 in that the other end of the auxiliary capacitor 25 is connected to the control line 35 (in which one end of the auxiliary capacitor 25 is connected to the source electrode of the driving transistor 22).

The pixel circuits 20A having this configuration are two-dimensionally arranged in a matrix form to form the pixel array unit 30. Here, for simplicity of illustration, only one pixel circuit 20A is shown. The control lines 35 are arranged with respect to the matrix of the pixel circuits 20A, and are wired along the pixel rows for each pixel row.

The organic EL display device 10 including the pixel circuit 20A according to example 1 includes a control scanning unit 90 serving as a control unit in addition to the write scanning unit 40 and the signal output unit 60 serving as peripheral circuits of the pixel array unit 30. For example, the control scanning unit 90 is disposed in a peripheral circuit region (frame region) on the same side as the write scanning unit 40 with respect to the pixel array unit 30. More specifically, the control scanning unit 90 is disposed in a peripheral circuit region on one side of the lateral direction (row direction) of the pixel array unit 30.

The other end of the auxiliary capacitor 25 is connected to the control line 35 of each pixel circuit 20A. One end of the control line 35 is connected to an output terminal of a corresponding row of the control scan cell 90. The control scanning unit 90 is configured by a shift register circuit or the like similarly to the write scanning unit 40. In synchronization with the line sequential scanning performed by the write scanning unit 40, the control scanning unit 90 outputs a control signal OS in an activated state for a period from the time after the threshold correction processing to the time before the writing processing of the signal voltage V_sig ends.

Preferably, the scanning line 31 transmitting the write scanning signal WS to the pixel circuit 20A and the control line 35 transmitting the control signal OS to the pixel circuit 20A are formed of the same wire material. Further, it is preferable that the scan line 31 and the control line 35 are formed to have the same thickness and width. The term "identical" herein means not only "exactly identical" but also "substantially identical". That is, various changes in design or manufacture are allowed.

Fig. 8 is a timing waveform diagram showing the circuit operation of the organic EL display device 10 including the pixel circuit 20A according to example 1. The timing waveform diagram of fig. 8 shows the variation of the waveforms of the power supply voltage (V_ccp/V_ini) DS, the write scan signal WS, the control signal OS, and the gate voltage V_g and the source voltage V_s of the driving transistor 22.

After the threshold correction process, the control scanning unit 90 switches the control signal OS supplied to the other end of the auxiliary capacitor 25 from the inactive state to the active state, that is, from the low voltage state to the high voltage state through the control line 35, thereby supplying a potential change to the other end of the auxiliary capacitor 25. Further, by providing a potential change to the other end of the auxiliary capacitor 25, the potential of the source electrode of the driving transistor 22 can be changed by means of coupling through the auxiliary capacitor 25, and the operating point of the driving transistor 22 can be set to the off-region.

After the threshold correction process, when the signal voltage V_sig is written by the write transistor 23, if the operating point of the drive transistor 22 is the off-region, the current I_ds does not naturally flow into the drive transistor 22. It is possible to eliminate a factor that fluctuates the source voltage V_s of the drive transistor 22 (this factor is different from the coupling associated with writing of the signal voltage V_sig). Therefore, there is no need to shorten the correction period (correction time), and thus there is no need to narrow the pulse width of the mobility correction pulse (the second pulse of the write scan signal WS).

In other words, since it is not necessary to shorten the correction period (correction time), the pulse width of the mobility correction pulse can be set wide. In the organic EL display device 10 including the pixel circuit 20A according to example 1, the pulse width of the mobility correction pulse that is the second pulse of the write scan signal WS is set to the same pulse width as the first pulse of the write scan signal WS. The term "identical" herein means not only "exactly identical" but also "substantially identical". That is, various changes in design or manufacture are allowed.

In this way, by setting the pulse widths of the two pulses at the time when the write scan signal WS enters the active state twice to be the same, the circuit configuration of the write scan unit 40 that generates the write scan signal WS can be simplified as compared with the case where the two pulse widths are different from each other. That is, when two pulses having pulse widths different from each other are generated, two logic circuits and the like for generating the respective pulses are required, but by setting the two pulse widths to be the same, one logic circuit and the like are sufficient, and thus the circuit configuration of the write scan unit 40 can be simplified.

(Operation of the circuit)

Next, a circuit operation (a method for driving a display device) of the organic EL display device 10 including the pixel circuit 20A according to example 1 will be described with reference to a timing waveform diagram of fig. 8.

Since the write transistor 23 is configured by an N-channel type transistor, the high voltage state of the write scan signal WS is an active state and the low voltage state thereof is an inactive state. Further, the write transistor 23 enters a conductive state in the write scan signal WS in an active state, and enters a non-conductive state in the write scan signal WS in a non-active state. In addition, for the control signal OS, the high voltage state is an active state, and the low voltage state is an inactive state.

In the light emitting state of the organic EL element 21, the power supply voltage DS is switched from the first power supply voltage V_ccp to the second power supply voltage V_ini at a time point t₂₁. Here, when the second power supply voltage V_ini is set to V_ini<V_thel+V_cath, the source voltage V_s of the driving transistor 22 becomes substantially the same as the second power supply voltage V_ini, and thus the organic EL element 21 enters a reverse bias state to be quenched.

Subsequently, since the write scan signal WS enters an active state at a time point t₂₂ (first pulse), the write transistor 23 enters an on state to write the reference voltage V_ofs to the pixel circuit 20A. Accordingly, the gate voltage V_g of the driving transistor 22 is initialized to the reference voltage V_ofs. Further, a period from a time point t₂₃ (at this time, the power supply voltage DS is switched from the second power supply voltage V_ini to the first power supply voltage V_ccp) to a time point t₂₄ (at this time, the write scan signal WS is converted from the activated state to the deactivated state) becomes a period for threshold correction.

Then, at a time point t₂₅ after the threshold correction process, the control signal OS is switched from the inactive state to the active state, that is, from the low-voltage state to the high-voltage state, and thus a potential change is supplied to the other end of the auxiliary capacitor 25. Accordingly, since the source voltage V_s of the driving transistor 22 changes due to coupling (capacitive coupling) through the auxiliary capacitor 25, the operating point of the driving transistor 22 becomes the off-region. Thus, the current I_ds does not flow into the drive transistor 22.

In the off state of the driving transistor 22, since the write scan signal WS enters the active state again at the time point t₂₆ (second pulse), the write transistor 23 enters the on state to write the signal voltage V_sig of the video signal into the pixel circuit 20A. Further, since the control signal OS is switched from the active state to the inactive state at the time point t₂₇, the driving transistor 22 enters the on state, the current Ids flows into the driving transistor 22, and the mobility correction process is performed.

Then, since the write scan signal WS is shifted from the active state to the inactive state at the time point t₂₈, the signal writing and mobility correction period is terminated, and the light-emitting period of a new display frame is started.

The above-described circuit operation is characterized in that, after the threshold correction process, a potential variation is supplied to the other end of the auxiliary capacitor 25, and by means of coupling through the auxiliary capacitor 25, a potential variation is supplied to the source electrode of the driving transistor 22, so that the operating point of the driving transistor 22 is set to the off-region. According to this circuit operation, when the signal voltage V_sig is written, since the current I_ds does not flow into the driving transistor 22, a factor that fluctuates the source voltage V_s of the driving transistor 22 (which is different from the coupling associated with writing of the signal voltage V_sig) can be eliminated.

Therefore, it is not necessary to shorten the mobility correction period. That is, it is not necessary to narrow the pulse width of the mobility correction pulse (the second pulse of the write scan signal WS). As a result, it is not necessary to form the pulse width adjustment circuit 80 (see fig. 5) for generating the mobility correction pulse having a narrow pulse width on the display panel 70, and thus the circuit size of the peripheral circuit of the pixel array unit 30 can be reduced. In addition, by reducing the circuit size of the peripheral circuit, the bezel can be narrowed, thereby minimizing the display panel 70.

Further, in the pixel circuit 20A according to example 1, the control scanning unit 90 is disposed in the peripheral circuit region on the same side as the write scanning unit 40 with respect to the pixel array unit 30. Accordingly, the distances from the write scanning unit 40 and the control scanning unit 90 to the pixel circuit 20A as a driving target can be set to be approximately equal to each other, and thus the timing deviation caused by the distance difference between the write scanning signal WS and the control signal OD can be minimized.

Specifically, the scanning line 31 that transmits the write scanning signal WS to the pixel circuit 20A and the control line 35 that transmits the control signal OS to the pixel circuit 20A are formed of the same wiring material, and have the same wiring thickness and the same wiring width. Accordingly, since the delay amounts at the time of transmitting the write scan signal WS and the control signal OD to the same pixel circuit 20A can be set to be approximately equal to each other, timing deviation between signals can be eliminated. Therefore, driving can be performed more reliably with respect to the pixel circuit 20A as a driving target. Here, it is assumed that the wiring material, the wiring thickness, and the wiring width are all the same, but not limited thereto.

EXAMPLE 2

Fig. 9 is a system configuration diagram showing an outline of the configuration of an organic EL display device including a pixel circuit according to example 2.

As shown in fig. 9, the pixel circuit 20B according to example 2 is configured to include a switching transistor 26 and a current control transistor 27 in addition to the organic EL element 21, the driving transistor 22, the writing transistor 23, the holding capacitor 24, and the auxiliary capacitor 25. The driving transistor 22, the writing transistor 23, the switching transistor 26, and the current control transistor 27 are formed of P-channel MOS transistors.

The pixel circuits 20B having this configuration are two-dimensionally arranged in a matrix form to form the pixel array unit 30. Here, for simplicity of illustration, only one pixel circuit 20B is shown. The control lines 35 are wired along the pixel rows for each pixel row with respect to the matrix arrangement of the pixel circuits 20B. Further, the first drive line 36 and the second drive line 37 are wired along the pixel row for each pixel row.

The organic EL display device 10 including the pixel circuit 20B according to example 2 includes a control scanning unit 90 serving as a control unit in addition to the write scanning unit 40 and the signal output unit 60, which are peripheral circuits of the pixel array unit 30. The control scanning unit 90 is disposed in a peripheral circuit region on the same side as the write scanning unit 40 with respect to the pixel array unit 30, more specifically, for example, in a peripheral circuit region on one side of the pixel array unit 30 in a lateral direction (row direction) in the drawing of the pixel array unit 30.

For each pixel circuit 20B, the other end of the auxiliary capacitor 25 is connected to the control line 35. One end of the control line 35 is connected to an output terminal of a corresponding row of the control scan cell 90. The control scanning unit 90 is configured by a shift register circuit or the like similarly to the write scanning unit 40. In synchronization with the line sequential scanning performed by the write scanning unit 40, the control scanning unit 90 outputs a control signal OS in an activated state (in this example, a low voltage state) for a period from the time after the threshold correction process to the time before the writing process of the signal voltage Vsig ends.

Preferably, the scanning line 31 transmitting the write scanning signal WS to the pixel circuit 20B and the control line 35 transmitting the control signal OS to the pixel circuit 20B are formed of the same wiring material. Further, it is preferable that the scan line 31 and the control line 35 are formed to have the same thickness and width. The term "identical" herein means not only "exactly identical" but also "substantially identical". That is, various changes in design or manufacture are allowed.

The organic EL display device 10 including the pixel circuit 20B according to example 2 further includes a driving scanning unit 91 and a current control scanning unit 92 as peripheral circuits of the pixel array unit 30. For example, the drive scanning unit 91 and the current control scanning unit 92 are provided in a peripheral circuit region opposite to the write scanning unit 40 and the control scanning unit 90, with the pixel array unit 30 interposed between the drive scanning unit 91 and the current control scanning unit 92 and the write scanning unit 40 and the control scanning unit 90. Here, the arrangement of the write scanning unit 40, the control scanning unit 90, the drive scanning unit 91, and the current control scanning unit 92 is only an example, but the present disclosure is not limited thereto.

The gate electrode of the switching transistor 26 is connected to the first drive line 36 of each pixel circuit 20B. One end of the first driving line 36 is connected to an output terminal of a corresponding row of the control scanning unit 91. The control scanning unit 91 is configured by a shift register circuit or the like similarly to the write scanning unit 40. In synchronization with the line sequential scanning performed by the write scanning unit 40, the control scanning unit 91 outputs a control signal AZ in an activated state for a period from the time before the start of the threshold correction process to the time at which the light emission is started.

The gate electrode of the current control transistor 27 is connected to the second drive line 37 for each pixel circuit 20B. One end of the second driving line 37 is connected to the output terminal of the corresponding row of the current control scanning unit 92. In synchronization with the line sequential scanning performed by the write scanning unit 40, the current control scanning unit 92 outputs a control signal DS which is in an inactive state (in this example, a high voltage state) for a period from the time when the threshold correction process is started to the time before the start of light emission and in an active state for a period different from the above-described period.

[ Circuit operation ]

Next, the circuit operation of the organic EL display device 10 including the pixel circuit 20B according to example 2 will be described with reference to the timing waveform diagram of fig. 10. The timing waveform diagram of fig. 10 shows the corresponding changes in the voltage (V_sig/V_ofs) of the signal line 33, the current control signal DS, the drive signal AZ, the write scan signal WS, the control signal OS, and the source voltage V_s, the gate voltage V_g, and the drain voltage V_d of the drive transistor 22.

Since each transistor of the pixel circuit 20B is constituted by a P-channel type transistor, the low voltage state of each of the current control signal DS, the driving signal AZ, the write scan signal WS, and the control signal OS is an active state, and the high voltage state thereof is an inactive state. Further, the write transistor 23 enters a conductive state in an activated state of the write scan signal WS, and enters a non-conductive state in a non-activated state thereof. The switching transistor 26 enters a conductive state in an active state of the drive signal AZ and enters a non-conductive state in a non-active state thereof. Further, the current control transistor 27 enters a conductive state in an activated state of the current control signal DS, and enters a non-conductive state in a non-activated state thereof.

In the timing waveform of fig. 10, a period from the time point t₃₁ to the time point t₄₂ is 1 horizontal period (1H). In a state in which the voltage of the signal line 33 changes from the light emission state of the organic EL element 21 to the reference voltage V_ofs, the write scan signal WS and the drive signal AZ enter the active state at the time point t₃₂, and thus the write transistor 23 and the switching transistor 26 enter the on state.

Accordingly, the reference voltage V_ofs is written to the gate electrode (V_g＝V_ofs) of the driving transistor 22. Here, since the current control transistor 27 is in an on state, the source voltage Vs of the driving transistor 22 becomes the power supply voltage V_ccp(V_s＝V_ccp). Accordingly, the supply of the drive current from the drive transistor 22 to the organic EL element 21 is stopped, and thus the organic EL element 21 enters an extinction state.

Then, the period from the time point t₃₂ to the time point t₃₃ (at the time point t₃₃, the current control signal DS is converted from the activated state to the deactivated state) becomes a period for extinction of the organic EL element 21, resetting of the source voltage V_s and the drain voltage V_d of the driving transistor 22, and preparation of the threshold correction process. During the period from t₃₂ to t₃₃, since the switching transistor 26 enters the on state, the power supply voltage V_ss is written to the drain voltage of the driving transistor 22 (V_d＝V_ss).

Then, while the write scan signal WS and the drive signal AZ are in the active state, the current control signal DS enters the inactive state and the current control transistor 27 enters the non-conductive state at a time point t₃₃ so as to start the threshold correction period. The threshold correction period becomes a period from the time point time t₃₃ to the time point t₃₄ (at the time point t₃₄, the write scan signal WS is converted into an inactive state).

Next, the control signal OS is switched from the inactive state to the active state, that is, from the high voltage state to the low voltage state at a time point t₃₅ to supply the other end of the auxiliary capacitor 25 with a potential change. Thus, the source voltage V_s of the driving transistor 22 is changed by coupling through the auxiliary capacitor 25, and thus the operating point of the driving transistor 22 becomes the off-region. Thus, the current I_ds does not flow into the drive transistor 22.

Then, the voltage of the signal line 33 is switched from the reference voltage V_ofs to the signal voltage V_sig of the video signal at a time point t₃₆. Since the write scan signal WS enters the activated state again at the time point t₃₇ and the write transistor 23 enters the on state, the signal voltage V_sig is input (written) into the pixel circuit 20B. Further, a period from the time point t₃₇ to the time point t₃₈ (at the time point t₃₈, the write scan signal WS is converted into an inactive state) is a signal writing and mobility correction period.

Then, since the control signal OS is switched to the inactive state at the time point t₃₉ and then the current control signal DS is switched to the active state at the time point t₄₀, the power supply voltage V_ccp is applied to the source electrode of the driving transistor 22, so that it becomes possible to supply the current to the driving transistor 22. Further, since the drive signal AZ transitions to the inactive state at the time point t₄₁, the light-emitting period of the organic EL element 21 starts. Then, since the voltage of the signal line 33 is switched from the signal voltage V_sig of the video signal to the reference voltage V_ofs at the time point t₄₂, the period of 1H is terminated.

Although the pixel circuit 20B according to example 2 described above has a larger number of parts than the pixel circuit 20A according to example 1, by using the organic EL display device 10 including the pixel circuit 20B, the same effect as that of the organic EL display device 10 including the pixel circuit 20A according to example 1 can be obtained.

That is, there is no need to prepare a mobility correction pulse having a narrow pulse width for mobility correction, and there is no need to form a pulse width adjustment circuit 80 (see fig. 5) for generating the mobility correction pulse on the display panel 70, and thus the circuit size of the peripheral circuit of the pixel array unit 30 can be reduced. Further, by reducing the circuit size of the peripheral circuit of the pixel array unit, the bezel can be narrowed, and thus the size of the display panel 70 can be reduced.

Further, in the pixel circuit 20B according to example 2, the control scanning unit 90 is disposed in the peripheral circuit region on the same side as the write scanning unit 40 with respect to the pixel array unit 30. Accordingly, the distances from the write scanning unit 40 and the control scanning unit 90 to the pixel circuit 20B as a driving target can be set to be approximately equal to each other, and thus the timing deviation caused by the distance difference between the write scanning signal WS and the control signal OD can be minimized.

Specifically, the scanning line 31 that transmits the write scanning signal WS to the pixel circuit 20A and the control line 35 that transmits the control signal OS to the pixel circuit 20B are formed of the same wire material and have the same wire thickness and the same wire width. Accordingly, the delay amounts at the time of transfer of the write scan signal WS and the control signal OS to the same pixel circuit 20B can be set to be approximately equal to each other, and thus the timing deviation between the signals can be eliminated. Therefore, driving can be performed more reliably with respect to the pixel circuit 20B that is the driving target. Here, it is assumed that the wire material, the wire thickness, and the wire width are all the same, but not limited thereto.

< Electronic device >

The display device according to the present disclosure described above can be used as any one of display units (display devices) of electronic devices in all fields in which a video signal input to the electronic device as an image or video or a video signal generated in the electronic device is displayed. For example, the display device may be used as any one of display units of electronic devices such as televisions, digital cameras, notebook personal computers, portable terminal devices such as mobile phones, video cameras, and head mounted displays.

In the electronic devices in all fields, by using the display device of the present disclosure as a display unit thereof in this way, the following effects can be obtained. According to the technology of the present disclosure, deterioration of uniformity due to conduction of the organic EL element during the mobility correction period can be suppressed, and thus image quality can be improved. In addition, a small-sized display panel can be manufactured, and thus reasonable yield can be improved. Accordingly, the cost of the electronic device including the display unit can be reduced. In addition, as the display panel becomes smaller, miniaturization of the device can be achieved, and thus the degree of freedom in design of a product (electronic device) can be increased.

The display device according to the present disclosure also has a module form configured to be sealed. For example, the module corresponds to a display module formed such that a facing unit such as transparent glass is attached to a pixel array unit. In the display module, a circuit unit or a Flexible Printed Circuit (FPC) inputting and outputting signals and the like between the outside and the pixel array unit may be provided. Hereinafter, a digital camera and a head mounted display are exemplified as specific examples of an electronic device using the display device according to the present disclosure. Here, a specific example is illustrated as an example only, and the present disclosure is not limited thereto.

(Specific example 1)

Fig. 11A and 11B are external views of a single-lens reflex digital camera with interchangeable lenses, in which fig. 11A shows a front view thereof and fig. 11B shows a rear view thereof. For example, a lens-interchangeable single-lens reflex type digital camera includes an interchangeable imaging lens unit (interchangeable lens) on the right front side of a camera body (camera body) 111, and includes a grip portion for a photographer to grip on the left front side.

A monitor 114 is provided at a substantially central portion of the back surface of the camera body 111. A viewfinder (eyepiece window) 115 is provided above the monitor 114. The photographer views the viewfinder 115, and thus can visually recognize the light image of the subject guided from the imaging lens unit 112 and determine the composition.

In the lens-interchangeable single-lens reflex digital camera having this configuration, the display device of the present disclosure can be used as the viewfinder 115. That is, the lens-interchangeable single-lens reflex type digital camera according to the present example is manufactured by using the display device of the present disclosure as the viewfinder 115.

(Specific example 2)

Fig. 12 is an external view of the head-mounted display. For example, the head-mounted display includes hooks 212 for mounting on both sides of the glasses display unit 211 on the head of the user. In the head-mounted display, the display device of the present disclosure may be used as the glasses display unit 211. That is, the head mounted display according to the present example is manufactured by using the display device of the present disclosure as the glasses display unit 211.

In addition, the present technology may also be configured as follows.

[1]

A display device, comprising:

A pixel array unit in which pixel circuits each including a light emitting unit, a writing transistor that writes a signal voltage of a video signal, a holding capacitor that holds the signal voltage written by the writing transistor, a driving transistor that drives the light emitting unit based on the signal voltage held by the holding capacitor, and an auxiliary capacitor having one end connected to a source node of the driving transistor, the pixel circuit having a function of threshold correction processing are arranged in a matrix form: the threshold correction process changes a source voltage of the driving transistor toward a voltage obtained by subtracting a threshold voltage of the driving transistor from an initialization voltage with reference to the initialization voltage of the gate voltage of the driving transistor; and

And a control unit that sets an operating point of the driving transistor to an off-region by supplying a potential change to a source electrode of the driving transistor through coupling via the auxiliary capacitor after the threshold correction process.

[2]

The display device according to [1],

Wherein the control unit changes the potential of the source electrode of the driving transistor by supplying the potential change to the other end of the auxiliary capacitor.

[3]

The display device according to [2],

Wherein the other end of the auxiliary capacitor is connected to a control line, and

The control unit switches a control signal supplied to the other end of the auxiliary capacitor from an inactive state to an active state through the control line to supply the potential variation to a source electrode of the driving transistor.

[4]

The display device according to any one of [1] to [3],

Wherein a source voltage of the driving transistor when the potential variation is supplied to the source electrode of the driving transistor is a voltage at least less than a sum of a cathode voltage of the light emitting unit and a threshold voltage of the light emitting unit.

[5]

The display device according to any one of [1] to [4],

Wherein the write transistor writes the signal voltage into the gate electrode of the drive transistor after the potential variation is supplied to the source electrode of the drive transistor.

[6]

The display device according to any one of [3] to [5], comprising:

A write scanning unit driving the write transistor by a scanning line in units of rows,

Wherein the control unit and the write scanning unit are disposed in a peripheral circuit region on the same side with respect to the pixel array unit.

[7]

The display device according to [6],

Wherein the control line and the scan line are formed of the same wiring material and have the same thickness and the same width.

[8]

The display device according to any one of [1] to [7],

Wherein a write scan signal enters an active state twice during the threshold correction process and during writing of the signal voltage, and

The pulse width of the two pulses when the write scan signal enters the active state twice is the same.

[9]

The display device according to [8],

Wherein the pixel circuit performs mobility correction processing of applying negative feedback to a potential difference between the gate electrode and the source electrode of the driving transistor at a correction amount corresponding to a current flowing in the driving transistor so as to correct mobility of the driving transistor in a period of a second pulse of the two pulses.

[10]

A method for driving a display device including a pixel array unit in which pixel circuits are provided in a matrix form, each of the pixel circuits including a light emitting unit, a writing transistor that writes a signal voltage of a video signal, a holding capacitor that holds the signal voltage written by the writing transistor, a driving transistor that drives the light emitting unit based on the signal voltage held by the holding capacitor, and an auxiliary capacitor having one end connected to a source node of the driving transistor, the pixel circuit having a function of threshold correction processing: the threshold correction process changes a source voltage of the driving transistor toward a voltage obtained by subtracting a threshold voltage of the driving transistor from an initialization voltage with reference to the initialization voltage of the gate voltage of the driving transistor, the method including:

When driving the display device, an operating point of the driving transistor is set to an off region by supplying a potential change to a source electrode of the driving transistor through coupling of the auxiliary capacitor after the threshold correction process.

[11]

An electronic device comprising

A display device, comprising:

A pixel array unit in which pixel circuits each including a light emitting unit, a writing transistor that writes a signal voltage of a video signal, a holding capacitor that holds the signal voltage written by the writing transistor, a driving transistor that drives the light emitting unit based on the signal voltage held by the holding capacitor, and an auxiliary capacitor having one end connected to a source node of the driving transistor, the pixel circuit having a function of threshold correction processing are arranged in a matrix form: the threshold correction process changes a source voltage of the driving transistor toward a voltage obtained by subtracting a threshold voltage of the driving transistor from an initialization voltage with reference to the initialization voltage of the gate voltage of the driving transistor; and

And a control unit that sets an operating point of the driving transistor to an off-region by supplying a potential change to a source electrode of the driving transistor through coupling of the auxiliary capacitor after the threshold correction process.

List of reference numerals

10 Organic EL display device

20. 20A, 20B unit pixels (pixel/pixel circuits)

21 Organic EL element

22. Driving transistor

23. Write transistor

24. Holding capacitor

25. Auxiliary capacitor

26. Switching transistor

28. Current control transistor

30. Pixel array unit

31 (31₁～31_m) Scanning line

32 (32₁～32_m) Power cord

33 (33₁～33_n) A signal line,

34. Public power line

35. Control line

36. First drive line

37. Second drive line

40. Write scanning unit

50. Power supply scanning unit

60. Signal output unit

70 Display panel

71-74 Input terminals

75. 76 Level shift (L/S) circuit

80. Pulse width adjusting circuit

81. Delay circuit unit

82. Gate circuit unit

83. Buffer circuit

90. Controlling a scanning unit

91. Driving a scanning unit

92. And the current controls the scanning unit.

Claims (9)

1. A display device, comprising:

A plurality of pixels, and

A control circuit;

Wherein each of the plurality of pixels includes:

A light emitting element including an anode and a cathode;

A capacitor;

a sampling transistor configured to supply a signal voltage from a data signal line to the capacitor according to a sampling control signal supplied through a sampling control signal line;

A driving transistor configured to supply a driving current from a first voltage line to the anode according to a voltage stored in the capacitor;

A first transistor electrically connected between the anode and a second voltage line;

A second transistor electrically connected between the first voltage line and the driving transistor; and

A voltage control element connected to a control line and configured to control a potential difference between a gate of the driving transistor and a source of the driving transistor according to a control signal provided by the control line, the control signal being switched between an inactive state and an active state within one horizontal period of a pixel operation;

the sampling transistor and the first transistor are configured to be turned on at a first timing, and

The sampling transistor is configured to be turned off a plurality of times during a first state in which the second transistor is in an off state, the first state being after the first timing.

2. The display device according to claim 1, wherein the voltage control element is electrically connected in series to the capacitor.

3. The display device according to claim 1,

Wherein the voltage control element is configured to control the potential difference between the gate of the driving transistor and the source of the driving transistor in accordance with a voltage control signal supplied through a voltage control signal line; and

The sampling control signal line and the voltage control signal line are formed to have the same thickness and width.

4. The display device according to claim 1,

Wherein the first transistor is configured to electrically connect the anode and the second voltage line according to a first control signal supplied through a first control signal line; and

The second transistor is configured to electrically connect the first voltage line and the driving transistor according to a second control signal supplied through a second control signal line.

5. The display device according to claim 1, wherein the sampling transistor, the driving transistor, the first transistor, and the second transistor are P-channel transistors.

6. The display device according to claim 1, wherein a potential of the first voltage line is higher than a potential of the second voltage line.

7. The display device according to claim 1, wherein the voltage control element comprises an auxiliary capacitor.

8. The display device according to claim 1, wherein the cathode is electrically connected to a third voltage line.

9. The display device according to claim 1,

The control circuit comprises a first control circuit and a second control circuit; and

The plurality of pixels are arranged between the first control circuit and the second control circuit.